NRC: ONOFRE OPERATOR FOLLOWED REGULATIONS

Nuclear safety regulators have determined the operator of the San Onofre plant followed procedures for design changes to replacement steam generators that later leaked radiation and have sidelined the plant for nearly six months.

The Nuclear Regulatory Commission on Thursday announced that Southern California Edison provided “all the information required under existing regulations about proposed design changes to its steam generators prior to replacing them in 2010 and 2011.”

Before leaving the nuclear commission this month, Chairman Greg Jaczko indicated that the agency would likely consider whether rules for reviewing replacement steam generators played a role in San Onofre’s problems and need revising. That evaluation has yet to occur, agency spokesman Victor Dricks said Thursday.

Dan Hirsch, a lecturer on nuclear safety issues at UC Santa Cruz, said regulators have effectively concluded that no one is at fault, while safety risks went undetected.

“Either they (Edison) violated the regulations or the regulations have holes large enough to drive a high-speed rail through,” Hirsch said.

Thursday’s report by a special team of NRC inspectors outlined in new detail how faulty computer modeling failed to predict conditions within the new steam generators, leading to the rapid degradation of tubing that circulates radioactive water through the core of the reactors at San Onofre.

Manufacturing issues also were cited as a cause for accelerated wear on tubes that vibrated against support structures and each other.

Members of the inspection team first discussed their findings at a public hearing a month ago in San Juan Capistrano.

Clusters of nearly 10,000 tubes serve as a crucial barrier to radiation releases and ensure the cooling of the reactor core.

The environmental group Friends of the Earth, aided by technical consultants, is the most prominent group to assert that Edison sidestepped a more rigorous license-amendment review of the generator design changes at San Onofre’s twin reactors.

Damon Moglen, a spokesman for the group, said the inspection report provided new evidence of the extent of design changes and the failure of regulators to fully recognize the risks they posed.

San Onofre has been shut down since Jan. 31, when a slow-flowing tube leak developed in the Unit 3 reactor, leading to a tiny release of radiation into the atmosphere that posed no health hazard.

That initial failure might have been much worse under the circumstances, the NRC report concluded.

“It is possible that a full-blown rupture could have been the first indication” of tube wear, the report said.

Inspectors also examined the potential for a combined tube rupture and steam-line break — a crucial measure of safety in pressured water reactors like San Onofre’s. Such an event would result in a major radiation release into the environment.

The new inspection results showed that three tubes failed testing that occurred at, or below, pressures associated with a break in a reactor’s main steam line. In all, eight tubes failed pressure tests.

In a written statement, Edison said Thursday that it continues to work on a plan for repairing and restarting San Onofre but gave no indication of timing. Any restart plan must satisfy a detailed list of requirements outlined by federal regulators.

Thursday’s report outlined how both reactors are susceptible to a phenomenon called “fluid elastic instability,” causing tubes to oscillate enough to rub against each other.

“The NRC team concluded that both units’ steam generators were of similar design with similar thermal hydraulic conditions and configurations,” the report said. “Therefore, SONGS Unit 2 steam generators are also susceptible to this phenomenon.”

The report also lists 10 major unresolved issues that still require study, including whether the generators were mishandled during shipping and amid early repairs.

The report defers judgment repeatedly on whether specific regulatory violations occurred until more information can be gathered.

The new steam generators were manufactured in Japan by Mitsubishi Heavy Industries. Mitsubishi’s analysis of what went wrong is still incomplete and will be evaluated as regulators consider Edison’s restart plan, the report said.

San Onofre’s generators were replaced at an initial cost of $671 million, shouldered by utility customers. In coming weeks, Edison is expected to update its cost estimates for reactor repairs and replacement power, as part of its public second-quarter earning report to investors.

The federal inspection team visited the plant for 10 days in March and spent months analyzing what they found.